1. Field of the Invention
The present invention relates to systems and methods for detecting position and/or orientation of a vehicle. More specifically, the present invention relates to systems and methods for minimizing error in inertial measurement units.
2. Description of the Related Art
Accidental or unauthorized attacks by nuclear-capable nations or attacks by rogue nations or terrorist groups, currently represent significant national security concerns. For this reason, a ‘layered’ missile defense has been recognized as being needed to protect U.S. and allied forces, as well as the U.S. homeland, from long-range, medium-range, and short-range air and missile attack.
Three segments are currently under development to support such a ‘layered’ defense: Boost Phase Defense, Midcourse Defense, and Terminal Defense. An element of the Midcourse Defense segment is Ground-based Midcourse Defense (GMD). The GMD is being designed and developed to protect all 50 U.S. states against limited ballistic missile attack by intercepting long-range ballistic missiles during the midcourse or ballistic phase of their flight, before their reentry into the earth's atmosphere.
The Raytheon kill vehicle represents a critical piece of the GMD program. The kill vehicle is the intercept component of the Ground-Based Interceptor (GBI) that includes a government choice of a booster. Its mission is to provide protection against small-scale missile attacks. Specifically, its niche in defense of the nation is to engage high-speed ballistic missile warheads, otherwise known as reentry vehicles, in the midcourse or exo-atmospheric phase of their trajectories and destroy them using only force of impact.
The Exo-atmospheric Kill Vehicle (EKV) is the intercept component of the Ground Based Interceptor (GBI), the weapon element of the Ground-based Midcourse Defense System. Its mission in the defense of the nation is to engage high-speed ballistic missile warheads in the midcourse phase of flight and to destroy them using only the force of impact or hit-to-kill.
The Exo-atmospheric Kill Vehicle (EKV) consists of an infrared sensor in a flight package used to detect and discriminate the reentry vehicle (incoming warhead) from other objects. The sensor includes a multiple-waveband infrared seeker that it uses to acquire and track targets. This seeker is comprised of focal plane arrays and a cryogenic cooling assembly attached to an optical telescope, supported by hardware and software processing. In addition to having an infrared seeker, the EKV has its own propulsion, communication link, discrimination algorithms, guidance and control system, and computers to support target selection and intercept decisions in the final seconds, or end game, of its flight.
The ‘hit-to-kill’ concept involves colliding with the incoming warhead, completely pulverizing it. This high-speed collision is intended to ensure complete destruction of a warhead carrying nuclear, biological or chemical weapons of mass destruction and the means of delivery, such as mid-range and long-range ballistic missiles. However, this high-speed collision requires accurate guidance and control. This is problematic inasmuch as the guidance is to be effected using an inertial measurement unit (IMU). Unfortunately, IMUs accumulate error over time. These errors affect the accuracy of the vehicle. That is, these errors limit the time of flight of exo-atmospheric vehicles.
To achieve longer exo-atmospheric flight times in accordance with conventional teachings, an IMU with low accelerometer and gyro biases is required to minimize errors in position, velocity, and attitude. However, such low bias IMUs can increase the cost of the system on the order of several hundreds of thousands of dollars. Further, even with these IMUs, velocity errors on the order of 10 m/s, position errors on the order of 5 km, and attitude error of 24 mrad can occur.
In the case of gyros, these errors are often compensated by the addition of stellar measurements, typically requiring a visible star sensor or stellar compass. However, the additional weight of these sensors can decrease system performance and increase cost considerably as well.
Hence, a need remains in the art for a system or method for increasing the accuracy of inertial measurement units used for exo-atmospheric and other high speed vehicles without substantially increasing the cost and/or weight thereof.